In general, multilayer ceramic capacitors have been fabricated by first preparing ceramic green sheets, printing a conductive ink for internal electrodes (composed of metal powder suspended in an organic vehicle) in the designed pattern on the ceramic green sheets, stacking several printed green sheets one on another under pressure, cutting the resultant stack into individual capacitor chips and, finally, firing the chips to complete multilayer ceramic capacitor units.
Most of the conventional dielectric ceramic materials for multilayer ceramic capacitors must be fired in an oxidizing atmosphere since they are reduced to a semiconductive material when fired in a neutral or reducing atmosphere with a low partial pressure of oxygen. Thus, a material for internal electrodes which is fired together with the dielectric ceramics is required to meet the following requirements: Firstly, it must not melt or evaporate at a sintering temperature of the ceramic dielectrics. Secondly, it must not oxidize or react with dielectrics even if the sintering is carried out under such a high partial pressure of oxygen that the ceramics is never reduced to a semiconductive material. Thus, it is required to use a noble metal such as, for example, platinum or palladium as a material for internal electrodes. However, the use of such a noble metal is an obstacle to reduction of the manufacturing cost of the multilayer ceramic capacitors and production of multilayer ceramic capacitors larger in capacitance but small in size.
For this reason, there is a craving to use a base metal such as, for example, nickel, instead of the noble metals for internal electrodes. To do this, it is required to develop a dielectric ceramic material which meets such requirements that it is never reduced to a semiconductive material even when fired in a neutral or reducing atmosphere with a low partial pressure of oxygen at 1360.degree. C. or less, and that is has a sufficiently high specific resistance and excellent dielectric characteristics required for ceramic dielectrics for capacitors.
In Japanese patent application laid-open No. 131708/1985, there is disclosed a nonreducible dielectric ceramic composition for temperature compensating capacitors which consists essentially of a solid solution expressed by the formula: EQU (Ca.sub.1-x Sr.sub.x).sub.m (Zr.sub.1-y Ti.sub.y)O.sub.3 +nMnO.sub.2
wherein the subscripts x, y, m and n take the following respective values: 0.ltoreq.x&lt;0.6, 0.ltoreq.y&lt;0.6, 0.85&lt;m&lt;1.30, and 0.005&lt;n&lt;0.08. The dielectric ceramic composition of this system can be produced by firing in a non-oxidizing atmosphere at a temperature of 1300.degree. to 1400.degree. C., thus making it possible to use a base metal as a material for internal electrodes of the multilayer ceramic capacitors. However, the dielectric constant of this dielectric ceramics is only 108 at the maximum, thus making it difficult to produce ceramic capacitors with a large capacitance without increase in volume.